This invention relates to lasers and, more particularly, to lasers of the vertical cavity surface-emitting type.
The development of vertical cavity surface-emitting lasers has made it possible to fabricate optical sources characterized by extremely small size and high output power. Additionally, multiple such sources can be conveniently integrated in a single chip to form two-dimensional arrays useful for a wide variety of optical information processing, interconnection and communication applications. Techniques for making and using such sources are well known in the art, as described, for example, in U.S. Pat. No. 4,949,350, entitled Surface-Emitting Semiconductor Laser, issued to J. L. Jewell and A. Scherer, and in an article by H. Orenstein, A. C. Von Lehmen, C. Chang-Hasnain, N. G. Stoffel, J. P. Harbison, L. T. Florez, E. Clausen and J. L. Jewell, entitled Vertical Cavity Surface-Emitting InGaAs/GaAs Lasers with Planar Lateral Definition, which appears in Appl. Phys. Lett. 56,2384 (1990).
Due to diffraction effects, the individual beams provided by the surface-emitting lasers of an integrated array exhibit a relatively high degree of divergence as they emerge from the planar output surface of the array. In practice, such divergence often causes deleterious effects such as crosstalk among the output beams to occur.
Accordingly, attempts have been made to focus or collimate the output beams of a vertical cavity surface-emitting laser array to avoid the practical problems caused by the divergence phenomenon. But heretofore all such efforts have involved the use of a separate lens array spaced apart from the laser array thereby to form a hybrid assembly for achieving the desired focusing or collimation.
The separate lens array included in such a hybrid assembly is typically bulky, difficult to fabricate, and difficult to maintain in precise alignment with the individual sources of the associated laser array. Hence, efforts have continued to try to devise other more suitable arrangements for controlling the output beams of a surface-emitting laser array. In particular, these efforts have been directed at trying to develop an easily fabricated, rugged, compact, microminiature assembly capable of both generating and shaping the laser output beams to exhibit the requisite focused or collimated shape.